The invention relates to the system and method for the decontamination of radiation contaminated equipment.
Stainless steel is widely used throughout the nuclear industry as a structural material and/or in equipment used for processes contacting nuclear materials. During such uses, the material or equipment can become grossly contaminated with radionuclides as is known in the art such that its usefulness is impaired. Primary contaminants might include: plutonium, americium, uranium and mixed fission products including cerium-144, ruthenium-106, cesium-137 and silver-110m. The equipment must then either be decontaminated, i.e., cleaned, stripped or the like of radionuclides, so that it can be returned to service or be disposed of by dismantling into small volumes for long term storage by burial or in a geologic repository. Failed equipment constitutes a large volume of contaminated radioactive waste which takes up a large volume of storage space, and is difficult to handle due to its radionuclide contamination. The ability to remove the contamination from the surfaces of metal equipment would greatly reduce the amount of waste requiring geologic disposal on the like and the costs associated with such disposal and monitoring of radioactive waste.
Recognizing the problem that this poses, a variety of cleaning solutions have been investigated for use in decontaminating equipment used in the nuclear industry. These solutions have included permanganate, oxalic acid, various detergents, inhibited mineral acids, and chelating agents as well as very corrosive materials like sulfuric acid, phosphoric acid, and hydrochloric acid, and combinations of other solutions. While these cleaning solutions worked to various degrees and can be used to decontaminate nuclear industry equipment to a certain extent, various problems still remain. Similarly, work is currently being done on using electrolysis in a phosphoric acid solution as a technique to decontaminate metals. This electrolysis is accomplished by making the metal piece to be decontaminated the anode and using a 40 to 80% phosphoric acid as a conductor or electrolyte. While this electrolytic process does have the advantage that it effectively decontaminates areas which are inaccessible to normal decontamination agents, it does have the drawback of employing solutions that cannot be easily regenerated, and it creates large volumes of high salt content liquid waste solutions with respect to the amount of material processed. Another disadvantage of this process is that the degree of decontamination of the piece of equipment is sensitive to the position of the cathode relative to the surface of the equipment.